An automotive air conditioner forms a refrigeration cycle by annularly connecting a compressor, a condenser, an expansion valve and an evaporator. The compressor adiabatically compresses gas refrigerant to form high-temperature, high-pressure gas refrigerant, and the condenser cools and condenses the high-temperature, high-pressure gas refrigerant by heat exchange with air outside the vehicle compartment. The condensed liquid refrigerant is adiabatically expanded by the expansion valve to thereby form low-temperature, low-pressure vapor refrigerant, and the vapor refrigerant is evaporated in the evaporator by absorbing heat from air in the vehicle compartment to form gas refrigerant, which is supplied to the compressor. By sequentially performing the above-mentioned operations, the temperature of air in the vehicle compartment is lowered.
The compressor used for the automotive air conditioner is driven by an internal combustion engine whose rotational speed is largely varied depending on the travel state of the vehicle, and hence a variable displacement compressor which is capable of discharging a constant amount of refrigerant irrespective of the travel state is employed. However, depending on the heat exchange conditions in the condenser and the evaporator, pressure changes in the refrigeration cycle become violent, and further, the state variation of the refrigerant also becomes large. For example, in a state where the evaporation capability of the evaporator is low, if high-pressure refrigerant flowing into the expansion valve is in a gas-liquid two-phase state, the refrigerant at an outlet of the expansion valve is also in the gas-liquid two-phase state. At this time, the refrigerant flowing through the valve section of the expansion valve is sometimes gas and sometimes liquid, which causes large pressure changes in the flow of the refrigerant. The pressure changes in the refrigerant cause the liquid level of liquid refrigerant remaining in the refrigeration cycle to rise and fall. Depending on the layout of piping, the liquid refrigerant sometimes blocks off a passage through which the gas refrigerant flows. In this state, if the gas refrigerant forcedly passes through the liquid refrigerant, big bubbles are generated, and when the bubbles burst, large noise is generated.
One known method of reducing such pressure changes in refrigerant as described above is to provide a throttle passage on an inlet side or an outlet side of an expansion valve (see e.g. Japanese Laid-open Patent Publication No. 2006-200844 and Japanese Utility Model Publication No. 07-52538). By providing the throttle passage on the expansion valve, it is possible not only to reduce pressure changes in the refrigeration cycle, but also to reduce noise of refrigerant flowing through the expansion valve by breaking the bubbles of refrigerant flowing therein into much smaller ones. Further, if the throttle passage is provided on the outlet side of the expansion valve, pressure reduction is performed twice, i.e. at the valve section of the expansion valve and at the throttle passage. This reduces the pressure difference at the valve section of the expansion valve, so that the generation of bubbles is suppressed, whereby it is possible to reduce noise of refrigerant flowing through the expansion valve.
However, the conventional throttle passage is formed by press-fitting a cylindrical throttle passage member having a through hole axially formed therethrough into a pipe, or by screwing the throttle passage member into a body of the expansion valve. This brings about problems that the cost of the throttle passage member made with precision is high, and that the fixing of the throttle passage member by press-fitting or screwing causes generation of foreign matter from a sliding surface of the press-fitted portion or the screwed portion, or damage to the press-fitted portion.